Kinematic Analysis of the Sidearm Throw in Ultimate Frisbee: Motion of the Wrist
1. Abstract The purpose of this study was to investigate the joint kinematics during the sidearm throwing motion. To date, little research has been conducted on the release parameters of the sidearm throw in Ultimate Frisbee. A kinematic three-dimensional high-speed analysis was conducted, measuring the joint angles of the forearm and wrist from the moment the pivoting foot came into contact with the ground until post release of the sports disc. A single male participant (Age; 20) case study was selected; with a minimum of three years of high level competitive Ultimate experience including participation in 3 National Student competitions. The subject was instructed to throw 35 slow (normal) and 35 fast (maximal effort) sidearm throws. Using two gen-locked Basler high-speed cameras at 200 Hz, released parameters were measured using reflective markers positioned at three points along the forearm; Medial Epicondyle of the Humerus, Styloid Process of Radius, Base of Metacarpals I-V. Mean (± standard deviation) wrist angles were found to be significantly (p<0.05) greater for fast trials (21.030 ± 2.937) than for slow trials (16.181 ± 2.847), however no significant difference was identified for spin rate between the two trials (fast: 6.650 ± 3.483, slow: 4.689 ± 1.730). A significant decrease in pronation angle and pronation angular velocity during the fast trials may be an important consideration suggesting that the initiation of throwing motion may occur from the shoulder The three-dimensional approach chosen for this study can provide valuable information on the kinematics of the sidearm throw for coaches and athletes, enabling training regimes and throwing techniques to be perfected.

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2. Introduction 2.1 Background Originally introduced during the Ancient Greek Olympics, the popularity of using a flying disc within sport has significantly increased during the last half century (Rhode, 2000). The technologies introduced during the Second World War led to the development of novel manufacturing procedures such as moulding. As a result, a prototype of the modern sports disc was created, with the Wham-O Corporation, California, trade marking the new invention as a ‘Frisbee’ based on the original ‘Frisbie Pie Tin’ (Rhode, 2000). At the present time, there are more Frisbees sold each year than the combined number of retailed baseballs, basketballs and footballs (Wham-O.com). The increasing demand for Frisbees has seen the introduction of many new exciting and competitive sports such as Ultimate and Disc Golf (Morrison, 2005). The limited offensive space in which to receive a throw therefore enhances the need for precision of passing required in Ultimate. This means that particular emphasis is placed on fine motor movements, all performed at very high speed, during disc release. Ultimate is primarily an invasion sport with the major emphasis placed on the ability of throwing. On a playing field 100 m long and 37 m wide, Ultimate is a dynamic, non-contact, team sport with similarities to netball, American football and basketball. The final 18 m of each end of the playing field are end zones, with a goal being scored when a team manages to successfully pass the disc to a team member located in the end zone that is being attacked. With no players able to run with the disc, successive passing is the only means to move the disc up field, whilst preventing the Frisbee from hitting the ground or being intercepted. What makes the sport of Ultimate Frisbee unique is the lack of a referee, allowing the sport to be based around the concept of the spirit of the game (Sasakawa & Sakurai, 2008)

An important variable when focusing on the mechanics of flight and in particular sports focusing on throwing is the release parameters associated with each individual sport and the athletes. As determined by Gemer, 1990; Lanka, 2000, to produce a throw in shot put at a competitive standard, the distance achieved will be defined by the direction in which the force is applied to the shot. Therefore ultimately the release velocity, angle of release and the height of release will determine the achieved distance. However where the release 4|Page

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velocity and release angle have to optimised, release height is not a significant variable within Ultimate. Release height in nearly all throwing sports is very influential to the throw outcome. In contrast, invasion sports such as American football and Ultimate are not influenced by genetic differences such as height and mass of a performer when determining throwing motions. The correct technique during build up and release of the sports disc remains the same for all competitors although individuals may adapt the general technique.

Strudarus (2003) identified a variety of adapted throws used by players during a competitive match including, the backhand throw, sidearm throw, hammer throw, scoober and blade. Sasakawa & Sakurai (2008) additionally identified that backhand and forehand (fig 1.) as the most frequently used throwing motions. The Throwing action required in Ultimate has been recognised as the most important skill, with players requiring sufficient ability to throw a variety of passes quickly and more importantly with accuracy. Due to the limited offensive playing space available during a match, the diversity of short passes and the occasional long pass (to accumulate points efficiently) results in players requiring sufficient practice of both short and long throws in training (Sasakawa & Sakurai, 2008).

2.1.1 Aims The purpose of this study was to develop a further understanding of the forearm joint kinetics building upon the three-dimensional analysis completed by Sasakawa & Sakurai (2008). The variables to be identified throughout the forehand throwing motion were; maximum and minimum values for the angle of pronation, pronation angular velocities, spin rate, disc linear velocities, wrist angles & wrist angular velocities. In addition, the identification of release parameters and attributes that occur between slow and fast release throws would provide future coaches and both novice and elite players with an innovative knowledge about forehand release mechanics. 2.2 Literature Review Upper limb and hand movements have been reviewed, in general, as complex (Murgia, 2005). The wrist has been defined as containing two degrees of freedom (DOF): radial/ ulna deviation and flexion/ extension (Metcalf, Notley, Chappell, Burridge &Yule, 2008). Literature has previously tried to identify the movement of the wrist; Miyata, Kouchi, Kurihara & Mochimaru (2004). Developing a computational model, the generation of joint angles of the thumb, fingers, hand and wrist were produced using single markers per joint. In addition, Small, Bryant, Dwosh, Griffiths, Pichora & Zee (1996) fabricated a surface marker model of the wrist using six markers. The study was able to conclude that methods for determining movement are difficult to improve in comparison to surface measurements. From the literature, it can therefore be suggested that there is no potential method of standardising the application of surface markers to the upper limb and forearm. As

identified in the study by Metcalf et al. (2008), measuring a wide surface area of the forearm/ upper limb increases the potential for markers to become occluded and indistinguishable. 2.2.1 Gyroscopic Effect When considering the flight of the sports disc, there are two main physical considerations determining the performance of Frisbee flight, aerodynamic lift and gyroscopic inertia (Morrison, 2005). The aerodynamic lift is proved by the airfoil design, essentially the same as an aircraft’s wing of smaller proportions, with the gyroscope acting as a stabilizer during flight providing that angular velocity is occurring. Morrison (2005) identifies the origin and importance of gyroscopic stability during the flight phase, concluding that rotation must occur to allow the mechanics of flight to occur. Although typically literature has focused on the fight mechanics of a backhand release, the main considerations during flight are the

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same. All the throws discussed in this study are of a right-handed forehand, resulting in an anti-clockwise disc rotation during flight, when observed from an elevated position. Assuming rotation is occurring, a lift force L is experienced perpendicular to the flat upper surface and velocity v / drag forces D.

Figure 2. Frisbee in flight, off-centre COP (Centre of Pressure) and COM (Centre of Mass) resulting in applied torque (as cited in Morrison, 2005). 2.2.2 Aerodynamic Lift & Pressure Lift, defined by Hummel (2003) is the perpendicular force to the flow of airstream that opposes the downward force of gravity. It can be assumed therefore that for the disc to travel horizontally in a balanced state, the lift force must be equal to gravity. As a disc travels through air, a fluid, the curved shape of the Frisbee deflects the oncoming flow, splitting the airstream above and below the disc (Panton, 1995). This separation of air, in addition to the cambered shape of the disc, results in the air flow above the disc travelling faster than the airflow below, causing a region of low pressure above the Frisbee (Hummel, 2003). A proportional relationship exists between increases in velocity and reduction of fluid pressure; Potts & Crowther (2002) have conducted complex studies measuring the changes in pressure for discs in flight. Data collected in previous studies have assumed aerodynamic patterns for a disc in flight, due to the difference in total velocities at each side of the disc when spinning. For example when a disc has been released from a forehand throw, due to the rotation (anticlockwise) the motion measured on the left (posterior view) will oppose the velocity of the disc, whereas the right will rotate in the same vector as the direction of the disc producing a greater total velocity. Previously, literature has failed to realise that

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when assuming lift will be reduced on the opposing edge, causing an incline or roll during flight, data repeatedly collected by Potts & Crowther (2002) significantly rejects this theory.

Due to the symmetrical design of the disc the COM will always be in the centre, however as displayed in Fig 2. the COP can become off-centre typically as a result of the natural incline of the front edge of the disc during flight (Hummel, 2003; Morrison, 2005). Torque is created due to the slight lift which is experienced at the exposed edge of the disc; when rotation does not occur, torque can cause the disc to flip upwards, effectively stopping any controlled flight to continue (Morrison, 2005). 2.2.3 Use of Reflective Markers Hummel & Hubbard (2001) conducted a study determining an appropriate musculoskeletal model of the backhand throw. Conducting kinematic analysis using 180 Hz high speed cameras, four subjects provided segment orientation data using reflective markers. Using known orthogonal coordinates of individual body segments measures for joint torque, motion phases and segment orientation were derived.

A more recent study by Sasakawa & Sakurai (2008) focused entirely on the forehand (righthanded) release parameters during a maximal effort throw. Using elite and non-elite subjects (N=17), the study tried to identify key differences in technique to provide valuable coaching feedback for novice players. All the experiments were performed in an indoor gymnasium, and analysis was conducted using two synchronized high-speed video cameras set at 250 Hz and a shutter speed of 1/2000 s. Subjects performed from an elevated position of 0.85 m allowing cameras to identify movement from beneath the disc flight, with the additional use of reflective markers positioned on anatomical landmarks along the throwing arm and cavity surface of the disc. The elite subjects that were used in Sasakawa & Sakurai (2008) study were reported as 6th place National championship qualifiers and members of a varsity Ultimate team with experience of 2-4 years. As the Ultimate team used in the study was based in Japan, little is known about the actual level of ability, and on reflection may not be at an elite level in comparison to European or American standards. In addition, little is stated about the nonelite athletes’ backgrounds and considering the amount of playing time that is actually spent throwing, maximal effort sidearm (forehand) throws are minimal. This therefore questions

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the study’s aim to provide coaching specific feedback for novice athletes, due to the lack of realistic data.

A study conducted by Gordon & Dapena (2006) aimed to measure the contributions of body segment motion in comparison to tennis racket head speed. The study conducted a 3D analysis and specifically focussed on the use of surface markers and joint centres to calculate accurate arm twist orientations. The researchers concluded from the research that the skinattached markers could not correctly identify and calculate upper arm twist orientation due to unforeseen skin movement. In addition, joint centre calculations produced levels of error exceeding 20%. Cappozzo, Catani, Leardini, Benedetti & Della Croce (1996); Reinschmidt, van den Bogert, Nigg, Lundberg & Murphy (1997) acknowledged that motion of skinmounted markers do not follow accurately the motion of the underlying bones. This inconsistency of accurate reflection of segment motion therefore compromises the potential accuracy of computed outputs through digitisation.

Gordon & Dapena (2006) employed biomechanical measures of participants to calculate elbow and wrist joint centres in contrast to the use of reflective markers. This could therefore arguably allow for more accurate results after computational analysis. However, the study only used a frame rate of 100 Hz; the authors did cite the need to minimise potential errors in manual digitising and suggested that a cut off frequency of 20 Hz would still allow high frequency detection as reasons for selecting a low frame rate.. An additional limitation of the study was identified by the authors regarding mechanical synchronisation of the cameras; the inability to exactly coordinate frames from different cameras may cause error during digitising.

As identified by Grabiner (1989); Palastanga, Field & Soames (1998) and Gordon & Dapena (2006) an important complication that may influence potential results, is the possibility of the elbow ‘carrying angle’ effect (Fig 3). When the elbow reaches full extension, the longitudinal axes of the upper arm and forearm may not be aligned. Potential angles of displacement can reach 10-15° in males.

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Figure 3. Model of the arm with a carrying angle at the elbow (as cited in Gordon & Dapena, 2006).

At present, literature has only focussed on the effects of the ‘carrying angle’ and the impact upon tennis serves. It becomes apparent that due to the unfamiliar motion during forehand throws in Frisbee, future studies may need to consider the negative impacts that this effect could place upon motion analysis. 2.6 Objectives The present study specifically focuses on the correlation between disc linear velocities and the distinction between wrist angle and spin rate between the fast and slow trials. It was hypothesised that a direct correlation between wrist angle and spin rate would occur between fast and slow trials. In addition, it was proposed that wrist angular velocity would increase for the fast trials accounting for increases in disc linear velocity. Null Hypothesis: No change would be found between fast and slow trials for spin rate, wrist angle and wrist angular velocity.

form; he was selected due to the high level of previous competitive performance; this specifically included participation in 3 National Student competitions, as a member of the varsity ultimate Frisbee team based at the University of Chichester (England) and a minimum of three years playing experience. 3.2 Equipment, Experimental Set-up & Design Testing was completed in an indoor facility, at the University of Chichester, to eliminate the effects of wind. All throwing trials were recorded using two gen-locked synchronised highspeed cameras (Basler, A602fc-2, Germany) at 200 Hz. The cameras were positioned in front of the subject, with a separation distance of 3.9m at angle of approximately 60°, and placed on tripods at a height of 2m.

Figure 4-6 illustrate the design of the steel rods with reflective markers attached. Figures 5, 6 display the forearm marker positions (5, frontal view; 6, posterior view) The reflective markers were securely attached to steel rods, positioned at three points along the forearm: Medial Epicondyle of the Humerus, Styloid Process of Radius, Base of Metacarpals I-V. To maximise the visual clarity during filming, reflective markers were attached to either a 20ml or 40ml steel rod, resulting in a maximum of five degrees of unwanted movement. This increase in rod length provided the maximum number of frames displaying the reflective markers, limiting the chances of cross-over or disappearance from view during motion. The steel rods were fastened to the skin of the forearm using high adhesive transpore tape, maintaining a rigid form and minimising potential movement during motion, preventing errors during filming. It is important to consider that there was no movement restrictions caused by the rod or tape placement. The total weight of the steel rods and reflective markers was 20g.

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Figures 7, 8, 9; reflective markers and extension arm placement on forearm and disc. The rods attached along the forearm were aligned orthogonal to each other, with the noncavity surface of the disc marked with three reflective markers at 120° to each other. A pretest was conducted to visually assess the disc performance prior and post attachment of the reflective markers. It was reviewed from footage that flight was not compromised by the additional weight of the markers. 3.3 Angle calculation & definitions of measured variables The hand (ulna-flexion) angle was measured with respect to the wrist; I.e. the angle between planes on the anatomical landmarks (W) and (H). Forearm pronation was digitally measured using the rotational translation between the planes (H) & (E). Setting up a datum using the virtual line between markers 7 & 8, the angle in a second position after 5 milliseconds (corresponding to a shutter speed of 200 Hz) was calculated.

Figure 11. displays the linear transformation of the disc and calculation of spin rate. Disc linear velocity was calculated from knowledge of the distance moved with respect to markers on the arm and change in time. 3.4 Safety Due to the concern over equipment safety and for the prevention of impacts received from high velocity discs, it was essential to use safety netting. All loose connecting wires were situated away from all testing areas, with mats on all flooring providing no potential risk of the subject tripping over exposed wires or debris. The position of the equipment was situated away from the line of flight of the sports discs, additionally minimising risks of impact. The high velocities throughout the movement phases resulted in all equipment such as reflective markers that had been connected to the subject, being thoroughly checked to ensure no possible breakdown would occur. The subject was correctly advised to wear sports specific clothing and footwear. 3.5 Protocol A SAQ warm-up, consisting of multiple throwing related movements and 20 trial throws was completed prior to testing and consent provided. Both camera positions and pre-test footage were analysed for quality and an 18-point calibration system was selected. The subject was instructed to throw 35 slow (normal) and 35 fast (maximal effort) release forehand throws using a 175 g, UKUA approved disc (Discraft Ultrastar, Michigan), without a run-up. A reference plate was provided on the floor for the subject to target foot placement. 13 | P a g e

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A direct linear transformation (DLT) methodology was used, as developed by Abdel-Aziz & Karara (1971). Three-dimensional coordinates of landmarks obtained from all video footage were computed. Digitising of all reflective markers (including disc) were completed for both camera angles. Due to image clarity, an optimum 15 trials were digitised for both the normal and maximal effort throws (Total Number = 30 trials). All 30 trials were initially cropped using an anchor event: ground contact of the unplanted foot, during the pivoting motion, from an initial standing position.

Figure 12. displays the experimental set-up. All digitizing was initiated using automatic tracking, however due to markers becoming occluded, manual digitizing had to be completed for specific frames. Manual digitizing, using a graphics interface, was also additionally conducted due to gross digitising errors occurring during automatic tracking. A single anchor point (disc release) was used when processing the output data; The mean square error for digital reconstruction was set at 0.5 cm, 0.5 cm and 0.7 cm for the x, y and z directions respectfully. 3.6 Statistical Analysis Paired samples t-tests were conducted to measure the differences in joint translations and disc flight between fast and slow trials using windows SPSS version 16. Statistical significance was set at P<0.05.

4.2 Subject throwing motion and follow through Figures 13-18 show the changes in release parameter traces throughout the throwing motion. Although significant differences were recorded between fast and slow trials, in general the motions were similar. Digital analysis was initiated from the marked event following ground contact with the pivoting foot, furthermore the forearm was observed at an angle of flexion roughly ≥90°. A significant difference in maximum pronation angle was observed pre-release. However, figure 13. clearly displays a symmetrical pattern between the fast and slow trials with a 15 | P a g e

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steady increase in supination peaking approximately 0.09s (slow) and 0.015s (fast) before release. This therefore indicates that there is an apparent cocking and unwinding phase figure 20. (phase’s 1-3). It can be observed that supination is occurring throughout the whole motion but the transition from maximum, prior to release and the immediate increase in forearm pronation during release can be identified as a major contributor to disc projection. In contrast to increased measures of pronation angle for the fast trials, statistics reported a significant difference for pronation angular velocity (forearm swing motion); the slow trials produced elevated levels of angular velocity in comparison to fast. Figure 14. displays the transformation for pronation angular velocity, the most substantial difference between the trials in addition to the increase in mean velocity (slow) is the length of time taken during the unwinding phase. Figure 14. visibly demonstrates that although the slow trials reported an overall increase in mean angular velocity, the unwinding phase for slow trials approximately lasts only 0.03s in contrast to 0.12s for fast trials.

Spin rate was reported as displaying no significant difference therefore, accepting the Null hypothesis. It is however, important to consider the mean values for the fast and slow trials and the range of standard deviation (Figure 19).

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4000 3500 3000 2500 2000 1500 1000 500 0 1 2

Figure 19. shows the mean (± standard deviations) of spin rate for the slow (1) & fast (2) trials. Due to large standard deviation within both the fast and slow trials a significant difference could not be obtained, however the mean values indicate that a difference may have occurred supporting the results of Sasakawa & Sakurai (2008).

5.0 Discussion 5.1 Cocking and unwinding phases It was identified that at time of foot contact with the ground, the forearm was initially in a supinated position with the palm facing anteriorly. The forearm was flexed at roughly 90° with the wrist additionally in flexion and adducted approximately 14°. Due to the chosen grip the subject’s fingers were both in a state of abduction between third and fourth metacarpal and adduction between the second and third metacarpal/ fourth and fifth. This positioning of the fingers allows the disc to pitch posteriorly, resulting in the frontal edge of the disc being lifted. During the cocking phase (Figure 20), supination of the forearm was increased in both slow and fast trials to an optimum point approximately 0.09s (slow) and 0.015s (fast) before release. Palmar flexion of the hand to a supine position occurs at the moment of peaked supination, with the elbow remaining in flexion. More importantly, at the peak moment of supination, due to palmar flexion and increased hand angle the disc was observed as being parallel to the midline of the forearm. This may be a significant moment in the build up to release of the disc, due to the disc angle of attack becoming parallel to the plane of motion.

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5.2 Throwing motion and disc release parameters Sasakawa & Sakurai (2008) identified an important trend for the angle of attack between skilled and unskilled performers. They reported that for the skilled performers the angle of attack was almost 0°, resulting in the disc being accelerated more smoothly during and postrelease due to minimal levels of air resistance. It was additionally identified that this allowed skilled performers to increase throwing distance despite similar initial velocities. The present study also supports the notion of disc release occurring parallel to the plane of movement (Figure 20). Linear velocities were noted to vary from the study conducted by Sasakawa & Sakurai (2008) who recorded initial linear velocities of 21.7 ± 1.7 (skilled); 20.7 ± 2.5 (unskilled) in contrast to 12.701 ± 1.221 for fast trials within the current study. The apparent large variation in linear velocities cannot be identified, it is however to note that the participants in study by Sasakawa & Sakurai (2008) were required to throw the disc as far as possible.

force production must have an additional source, other than pronation angle & angular velocity.

Sasakawa & Sakurai (2008) reported small ranges of pronation angles for skilled throwers and in addition, identified that disc spin rate was unlikely to have been produced directly from a pronation motion of the forearm. However, indirectly it was reported that pronation just prior to release enabled a more effective range of plantar flexion motion. This increased plantar flexion was believed to provide greater spin rate to the disc. The current study further identified an increase in pronation just prior to release and in fast trials identified a significant increase in plantar flexion (hand angle), supporting the findings of Sasakawa & Sakurai (2008). It was however found that no significant difference was reported for spin rate between fast and slow trials. As previously identified, it is important to recognise the results (Figure 19) clearly display spin rate having an increased mean for fast trials, however an increase in trials may have provided clarity. No significant difference was observed for angular velocity of the hand in relation to the wrist (plantar flexion motion) between trials. This therefore, accepted the Null hypothesis, suggesting that disc linear velocity was not a resultant of plantar flexion.

The series of forearm motions just prior to disc release were identified as an increase in pronation from a supinated position, wrist extension and ulnar flexion from a radial position. The elbow was in a motion of extension from an initial flexed position. Stancil (1975), Danna & Poynter (1979) describe the release motion or ‘snap’ in coaching manuals as a sequential motion consisting of supination of the forearm and ulnar deviation of the wrist. Although this is supported by the results of the current study, it is important to recognise that positive pronation does not occur; simply supination is decreased by a pronation motion. At the point of release supination is reduced but still evident. Sasakawa & Sakurai (2008) additionally describe the ‘snap’ as the sequential motion consisting of supination of the forearm and ulnar deviation of the wrist. This evidence suggests that the sequence of motion comprised of palmer flexion and ulnar deviation after dorsi flexion and radial deviation, respectively.

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From the results of this study there is a clear indication that development of forward momentum needed to project the disc linearly, at any given velocity, must be initiated in addition to the motion of the forearm and wrist. This is due to no significant difference being identified between the hand angular velocity and pronation angular velocity variables. Sakurai, Ikegami, Okamoto, Yabe & Toyoshima (1993) identified the following motion during the acceleration phase of baseball pitching: rapid shoulder internal rotation, elbow extension, ulnar flexion and pronation. This series of sequential motions strongly reflects those acknowledged in the both the current study and in the findings of Sasakawa & Sakurai (2008). Therefore, it can be proposed that the Ultimate Frisbee forehand throw strongly resembles the overhand throw in baseball pitching. Additionally, Feltner & Dapena (1986) documented the shoulder and elbow motions, 0.2s prior to release in baseball pitching using a 3D analysis. They reported that internal rotation of the shoulder and extensions of the elbow were important attributes to the success of pitching motions. A more recent study by Dillman, Fleisig & Andrews (1993) also identified internal rotation of the shoulder, extension of the elbow, pronation of the forearm & ulnar deviation of the wrist just prior to release when focussing on joint kinematics of the forearm during baseball pitching. From literature it can therefore be suggested that force production and shoulder motions are key to the differences in disc linear velocities, with the additional use of the forearm and wrist to help provide stability during unwinding and release phases.

In contrast, Aguinaldo, Buttermore & Chambers (2007) conducted a study focussing on the shoulder joint torques within baseball pitching. In addition to using a three-dimensional protocol using reflective markers, it was discussed that transfer of momentum would require less contribution of distal body segments. Additionally, Putnam (1991; 1993) and Bahamonde (2000; 2005) concluded that baseball pitching like other throwing activities uses momentum sequentially initiated from larger body segments. These larger body segments collectively with smaller distal segments contribute to overall force and velocity output of a throw. However, although applicable and accounting for most throwing motions, it is important to note that the forehand throw in ultimate does not directly follow this rule. Sasakawa & Sakurai (2008) conclude that although a possible analogous relationship between baseball pitching and sidearm throwing in ultimate may occur, marked differences in shoulder abduction/ adduction and pronation/supination of the forearm were apparent.

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However, it was additionally suggested that this may have been as a resultant of the size and shape of the projectile and grip required to throw.

5.3 Future considerations In the current study a single subject protocol was used to test the methodology of 3-D kinematics, although may not be universally applicable, relevant differences between variables should be highlighted. A future direction may be to use a cohort of athletes, including a variation in technical ability to help identify trends between release parameters that maybe apparent. This in turn could assist coaches in identifying correct techniques or additionally, comprising efficient exercises in practice to progress athletes on both a team and individual level. Furthermore, it is important to identify the differences between coaching manuals and previous literature when regarding release parameters. It is apparent that little or no kinematic analysis has been achieved in an outdoor environment and given the influences of external factors such as wind, as this may have a major impact on release parameters. This study does however provide evidence that 3-D kinematics can be administered as an effective tool for measuring disc release techniques.

Coaches and performers may be at the risk of stress injuries caused to the medial side of the elbow due to large tensile forces produced by shoulder internal rotation torque (Bahamonde, 2005). Elbow injury has previously been identified within tennis forehand strokes (Bahamonde, 2005) and baseball pitching (Sakurai et al., 1993); due to the evidence of an analogous relationship with the sidearm throwing motion in ultimate, future deliberation may be required. Sakurai et al. (1993) furthermore concluded that multiple baseball pitching is thought to increase the risk of elbow injury. Additionally, if the athlete begins throwing at an early age, which is currently occurring in Ultimate as popularity and recognition of the sports increases, there is a greater risk (Morrison, 2005).

6.0 Conclusion The sidearm throw in Ultimate Frisbee was explored using 3D kinematic analysis of forearm joint angles. The findings from this research build on and are corroborative with the previous study by Sasakawa & Sakurai (2008). Increased hand angle at the point of release, with respect to the wrist, was shown to be significantly greater for higher disc release rates.

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Furthermore, just prior to release the forearm and wrist motions displayed pronation from an initial supinated position, palmar flexion, extension at the elbow and plantar flexion. Spin rate was found not to display a significant difference between fast and slow disc release rates; however errors during the digitising process may have masked subtle differences. The three-dimensional approach chosen for this study can provide coaches and athletes with the capability to gain a clearer understanding of the kinematics of the sidearm throwing motion. It is however, important to acknowledge individual differences in technique could vary and the study was only conducted with a limited resource.

Acknowledgements

I would like to dedicate this research project to my family; Andy, Trisha, Nicola, Hollie, Jenny, Avalon & Rupert. I wish to thank James Nairn for his participation in the study and the support from Jenny Feakins throughout. I would also like to thank my project supervisor Neal Smith for his guidance, support and interest throughout the study.